Variable resistor with improved housing cover securement



Oct. 22, 1957 w. A. BARDEN VARIABLE RESISTOR WITH IMPROVED HOUSING COVER SECUREMENT Flled Aprll 6, 1956 United States PatentOfiice Patented Oct. 22, 1957 VARIABLE RESISTOR WITH IMPROVED HOUSING COVER SECUREMENT Wayne A. Barden, Elkhart, Ind., assignor to Chicago Telephone Supply Corporation, Elkhart, Ind., a corporation of Indiana Application April 6, 1956, Serial No. 576,691

1 Claim. (Cl. 201-55) This invention relates to variable resistors and similar electrical control instrumentalities, of the type having a rotor enclosed within a housing and actuatable by means of a shaft which projects forwardly from the housing.

Small variable resistors of the type used in radio and television receivers commonly have a substantially cylindrical housing with flat front and rear walls connected by a cylindrical side wall. The mechanism of the resistor is enclosed within this housing and generally includes a fixed resistance element and a metal collector ring, and a rotatable contactor bridging the resistance element and collector ring and drivingly connected with an actuating shaft which is usually journaled in a bushing carried by the front wall of the housing. The control shaft, of course, projects forwardly from the bushing to be accessible for manipulation.

The specific construction of the housing employed for variable resistors is usually dictated by the use for which the resistor is designed, and in its most common form generally consists of a base of insulating material upon the rear face of which the resistance element and collector ring are mounted, and a stamped cup-shaped metal cover secured to the base and covering its rear face. Often, however, the front wall of the housing through which the shaft projects is integral with the cylindrical side Wall, and in this case, the rear housing wall is simply a flat disc-like cover having its peripheral edge seated upon the side wall. it is resistors having housings of the latter type with which this invention is specifically concerned.

Heretofore it has been conventional practice in such resistors to secure the cover in place across the back of the cup-like housing body by means which entailed a special manufacturing or assembly operation devoted exclusively to such securement.

Bearing in mind that variable resistors used in radio and television receivers must meet rigid performance and size specifications, and that low manufacturing costs are so essential that the smallest fraction of a cent per unit is critical, it is an object of this invention to eliminate the need for a special manufacturing or assembling step in the securement of the cover of a variable resistor housing.

Another object of this invention resides in the provision of cooperating means directly on the rear housing cover and on the rotatable control shaft of a control instrumentality of the character described for holding the cover in place across the back of the housing, and which cooperating means are readily engageable with one another without the use of special tools or equipment and without the need for any special skill or even a high order of manual dexterity.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claim, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claim.

The accompanying drawing illustrates one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

Figure l is a longitudinal sectional view of a variable resistor embodying this invention;

Figure 2 is a rear elevational view of the resistor shown in Figure 1, a portion of the cover being broken away to show details of construction, and;

Figure 3 is a group perspective view of the cover and the rotatable element of the variable resistor shown in Figures 1 and 2, a portion of the rotatable element being broken away and shown in section.

Referring now to the accompanying drawing, the numeral 5 designates generally a control instrumentality, which, for purposes of illustration, is shown as a variable resistor and which comprises a cylindrical housing 6 enclosing a rotatable contactor 7 carried by a shaft 8 extending coaxially through the housing and projecting forwardly therefrom to be accessible for manipulation.

The housing comprises a cup-like shell or body having a front Wall 10 and a cylindrical side Wall 11 integral with and projecting rearwardly from the front wall. This shell may be formed as a metal stamping provided with suitable insulation on the interior thereof or (as shown) as a molding of insulating material. In the variable resistor shown,,a strip 12 of resistance material overlies the inner surface of the housing side wall and a conductive collector ring 13 is coaXially seated upon the rear face of the front wall. Suitable terminals 14 and 15, connected with the resistance strip and collector ring, respectively, extend to the exterior of the housing to permit securement thereto of conductors (not shown). The cup-shaped shell is closed by a disc-like closure or cover 16 which extends across the rear of the housing and is secured in place in the novel manner hereinafter described.

The shaft is rotatably journaled in a bushing 17 coaxially mounted in the front wall and long enough to prevent lengthwise tilting of the shaft. The contactor comprises an insulative carrier 18 secured to the shaft for rotation therewith and a stamped metal spider 19 secured to the carrier by means of lugs 20 on the spider bent around opposite edge portions of the carrier. The spider has integral spring fingers 21 and 22 projecting from the body thereof to have wiping engagement with the resistance strip and the collector ring, respectively.

Good contact between the fingers 21 and the resistance strip is assured by so forming these fingers that to effect insertion of the rotor into the housing body the fingers must be sprung or forced radially inward; and to assure satisfactory contact between the fingers 22 and the collector ring the rotor is secured against rearward axial displacement from a position at which the fingers 22 are under a predetermined spring tension. Any suitable means may be employed to restrain the rotor against rearward axial displacement, as for instance, a C-washer 23 engaged in a groove in the shaft 8 and bearing against the front end of the bushing 17.

The shaft extends rearwardly through the housing and has its rear end portion projecting beyond the cover 16 through a substantially keyhole-shaped aperture 24 therein. A short distance ahead of its rear end, the shaft has a circumferential groove 25, the width of which is slightly greater than the thickness of the cover and the depth of which is such that the small end of the key hole 24 snugly accepts the neck 26 formed by the bottom of the groove.

When in position the disc-like cover 16 is received in a shallow counterbore 27 at the rear end of the body side wall 11, the bottom 28 of which is on a plane so spaced from the front end of the bushing 17 which defines the axial position of the shaft, that the forwardly facing side 29 of the groove in the shaft is forwardly of the plane of the bottom 28 of the counterbore. Accordingly, when the cover is in place with its peripheral portion seated on the bottom of the 'counterbore and the small end of its keyhole-shaped aperture 24 embracing the neck 26 and its rear face bearing against the side 29 of the groove, the cover will be slightly dished in and thus sprung out of its normal fiat state and under tension. This manner of holding the cover in place thus not only meets the objective of the invention which is to obviate the need for a special manufacturing or assembly step in the securement of. the cover, but in addition achives a desirable tightness for the closure.

As will be recognized from the drawing, the keyholeshaped aperture 24 in the cover is defined by a pair of intersecting round holes of different sizes, the greater of which is large enough to receive the full shaft diameter and is eccentric to the shaft axis when the cover is assembled to the housing, and the lesser of which, as stated, is of a size to accept the neck 26 of the shaft and is concentric thereto when the cover is in place. Hence, application of the cover entails slight edgewise shifting thereof from its position in which it is engageable over the rear end of the shaft, and to enable such shifting of the cover its central portion bounding the keyhole-shaped aperture of course must be depressed to align with the groove 24. To accommodate such depression or flexure of the cover, the material from which it is made should possess substantial resilience. Bakelite and other similar insulation has been found suitable.

Obviously, when the cover is brought into coaxiality with the shaft, it snaps down into the counterbore.

Removal of the cover may be easily effected by prying up its edge nearest the small end of the keyhole shaped aperture and sliding the cover edgewise over the rear edge of the counterbore.

To accommodate the resistance strip terminals 14 which project rearwardly from the interior of the housing, the cover has suitably located notches 30 in its edge, and to hold the cover against rotation from a position at which the notches are properly aligned with the terminals without placing any strain upon the terminals, the cover has a notch 31 in which a locating [1 lug 32 on the rear of the housing side wall is snugly received.

From the foregoing description taken together with the accompanying drawing, it will be apparent that this invention achieves its purpose in a very simple and direct manner entirely consonant with the ever present objective of this art, namely reduction in production costs without sacrificing quality.

What is claimed as my invention is:

In a variable resistor of the type comprising a housing having a front wall, a substantially cylindrical side wall projecting rearwardly therefrom and a disc-like cover closing the rear of the housing, a fixed resistance element in said housing spaced forwardly from the rear edge of the housing sidewall, terminals for the rcsistance element projecting rearwardly from the housing at the inner edge of the housing side wall, a shaft rotatably journaled in a bearing carried by the front wall of the housing and restrained against rearward axial displacement and a movable contactor carried by the shaft and eooperable with the resistance element, means for securing the cover in place comprising: a rearwardly facing shoulder on the housing side wall provided by the bottom of a counter-bore in the housing side wall, said shoulder being spaced rearwardly of the resistance element, and the diameter of the counter-bore being slightly larger than the diameter of the cover; the edge portion of the cover being received in the counter-bore to be held thereby against lateral and forward axial displacement relative to the housing side wall, the edge of the cover having notches to accommodate 'the terrninals; cooperating interengaged abutments on the edge of the cover and the housing side wall to properly locate and hold the cover against radial displacement with its notches aligned with and receiving the terminals; and cooperating abutment means on the cover and on the rear portion of the shaft precluding rearward axial movement of the cover relative to the shaft, said abutment means being provided by a keyhole-shaped hole in the cover through which the rear portion of the shaft projects and a circumferential groove in the shaft defining a neck and a forwardly facing shoulder, the neck being received in the smaller portion of the keyhole-shaped hole.

References Cited in the file of this patent UNITED STATES PATENTS Schellenger Nov. 18, 1930 Daily et al Nov. '17, 1953 

